DESCRIPTION: The proposed experiments are intended to clarify how humans make use of the various different cues to depth. Three themes guide this work. The first is that an ideal observer is sensitive to the quality of information available from different depth cues in a particular scene. The second is that the ideal observer is sensitive also to the logical type of information available from different depth cues. Depth information of different types must be promoted to a common type before being combined, and this process may explain many depth cue interactions. The third theme concerns the veridicality of stimuli. If an ideal observer is sensitive to the quality of information available from different depth cues then the use of impoverished stimuli can alter the nature of the processing. These three themes lead to a Modified Weak Fusion framework for understanding depth cue combination. The experiments will use highly realistic, controllable viewing conditions involving large displays and accurately modelled scene and surface properties. The proposed research consists of three major tasks: 1) Examination of interactions between depth cues in terms of perceived depth as well as other perceived surface properties such as lightness to test the MWF model 2) Carry out a number of single cue depth studies and other control studies and 3) Study the form of the surface representation used by human observers.